Abstract
In the integrated planar solid oxide fuel cell (IP-SOFC) design individual cells are printed on a porous substrate and connected in series. This minimises the costs by using minimal amounts of functional materials, coupled with mass production techniques. However, the configuration is unfavourable in terms of current collection from the electrodes. From a survey of potential materials for the anode current collector, nickel (from the in-situ reduction of nickel oxide) was identified as the most promising material in terms of cost, availability and the environmental impact compared with the precious metals that are used currently. A novel composite anode microstructure, consisting of small nickel oxide tracks printed within a nickel oxide/yttria tracks doped zirconia anode, was found to provide a level of in-plane conductivity suitable for use in the IP-SOFC. There were, however, issues with the use of nickel oxide. It was found to migrate and react with the magnesium oxide from the support tube, to form a solid solution during sintering of the fuel cell layers. Furthermore, the presence of nickel oxide was found to cause grain growth and phase changes in yttria doped zirconia at high temperatures the extent of which was dependent on the yttria content. For 3 mol% yttria doped zirconia, nickel oxide was found to cause rapid grain growth and stabilise the cubic phase at lower yttria concentrations. Additionally nickel was observed to migrate over 200 mum through the zirconia samples in one hour at 1500°C. For the 8 mol% yttria doped zirconia, which was predominantly cubic initially, the nickel oxide also caused rapid grain growth but the nickel migration was confined to a depth of approximately twice the size of the large grains. The problems associated with nickel oxide are only significant at the high temperatures used during manufacture, so if these can be reduced or eliminated then the benefits a nickel based anode current collector could be realised.